Copper alloy

ABSTRACT

A copper alloy subjected to a thermo-mechanical treatment and composed of (in wt %) 15.5 to 36.0% Zn, 0.3 to 3.0% Sn, 0.1 to 1.5% Fe, optionally 0.001 to 0.4% P, optionally 0.01 to 0.1% Al, optionally 0.01 to 0.03% Ag, Mg, Zr, In, Co, Cr, Ti, Mn, optionally 0.05 to 0.5% Ni, the remainder being copper and unavoidable contaminants, wherein the microstructure of the alloy is characterized in that the proportions of the main texture orientations are at least 10 vl % copper orientation, at least 10 vl % S/R orientation, at least 5 vl % brass orientation, at least 2 vl % Goss orientation, at least 2 vl % 22RD-cube orientation, at least 0.5 vl % cube orientation, and finely distributed iron-containing particles are contained in the alloy matrix.

The invention relates to a copper alloy.

Electronic components, including terminal contacts, form the foundationof information technology. One of the most important considerations ineach terminal contact is optimization of the embodiment at the lowestcosts. With the continuous price pressure, the demand exists in theelectronics industry, inter alia, for alternative materials to suchmaterials, which have the desired properties and which are alsocost-effective. Desired properties of an alloy are, for example, highelectrical and thermal conductivity and also high stress relaxationresistance and tensile strength. Typically, copper alloys are used asterminal clamps and also for other electrical and thermal applications,because of the generally outstanding corrosion resistance thereof, thehigh electrical and thermal conductivity, and the good storage and wearqualities. Copper alloys are also suitable because of the good coldmachining or hot machining properties thereof and the good deformationproperty thereof.

A copper alloy is known from the publication EP 1 290 234 B1, whichalready displays a more cost-effective alternative to otherwise typicalcopper alloys having high electrical conductivity, high tensilestrength, and high shaping strength. The alloy consists of 13 to 15%zinc, 0.7 to 0.9% tin, 0.7 to 0.9% iron, and a residual balance ofcopper. As a result of the zinc, having a comparatively low metal valuecurrently on the market, costs can be saved in the base material.

A copper alloy, which has a zinc proportion of at most 15.0%, is knownfrom the patent specification U.S. Pat. No. 3,816,109. The iron contentis between 1.0 and 2.0%. Using this composition, a comparatively goodelectrical conductivity is achieved in conjunction with sufficienttensile strength.

Furthermore, copper-tin-iron-zinc alloys are known from the patentspecification U.S. Pat. No. 6,132,528, which have a higher zinc contentof up to 35.0%. The iron proportion is between 1.6 and 4.0%. Theaddition of iron has the function of achieving grain refinement alreadyafter the casting.

The invention is based on the object of refining a copper alloy in sucha manner as to refine it with respect to the stress relaxationresistance and further material properties. In particular when processedas a strip material, the alloy is to be oriented to the technicalproperties of the bronzes CuSn4 (C51100) and CuSn6 (C51900), with a lowmetal value at the same time. In addition, the manufacturing pathway isto be made as simple as possible. With respect to the tensile strength,values are to be 600 MPa, the electrical conductivity is to be at least20% IACS. In addition, the copper alloy processed as strip is to be wellbendable and is to be able to be used as a spring material.

The invention is represented by the following features, advantageousembodiments and refinements.

The invention includes a copper alloy, which was subjected to athermomechanical treatment, consisting of (in wt.-%):

15.5 to 36.0% Zn,

0.3 to 3.0% Sn,

0.1 to 1.5% Fe,

optionally 0.001 to 0.4% P,

optionally 0.01 to 0.1% Al,

optionally 0.01 to 0.3% Ag, Mg, Zr, In, Co, Cr, Ti, Mn,

optionally 0.05 to 0.5% Ni,

the remainder copper and unavoidable impurities, wherein themicrostructure of the alloy is characterized in that the proportions ofthe main texture orientations are

at least 10 vol.-% copper orientation,

at least 10 vol.-% S/R orientation,

at least 5 vol.-% brass orientation,

at least 2 vol.-% Goss orientation,

at least 2 vol.-% 22RD cube orientation,

at least 0.5 vol.-% cube orientation, and

finely distributed ferrous particles are contained in the alloy matrix.

The copper alloy according to the invention primarily relates to strip,wire, or tubular material, having as the main components copper, zinc,tin, and iron. The zinc content between 15.5 and 36.0% is selected inthe alloy in particular according to the criterion that a single-phasealloy which can be easily shaped is obtained. The single-phase basemicrostructure consists of alpha phase. The base microstructure mustalso be suitable for absorbing the finest possible precipitants of otherelements. It has been shown that the zinc content should not exceed36.0%, since otherwise a less favorable phase composition results in thealloy. In a preferred embodiment, a zinc content of at most 32.0% is notexceeded. In particular in the case of zinc contents which exceed thespecified value, the brittle beta phase occurs, which is undesirable inthis context. On the other hand, extensive experimental results of analloy variant having 30.0% zinc have shown that the desired propertiesare still ensured. An important property of the alloy is its resistanceagainst stress relaxation and stress crack corrosion. On the other hand,economic aspects are also to be mentioned in the solution according tothe invention. Thus, the element zinc can still currently be purchasedat a reasonable price in the market and is available, in order to thusproduce alloys which are more favorable in the metal price, theproperties of which at least extend to heretofore known alloys. Thus,the alloys according to the invention have a lower metal value thanconventional copper-tin-phosphor alloys. The material properties arealso to be oriented to these alloys.

From a technical aspect, a higher tin content in the alloy according tothe invention affects the strength and the relaxation resistance. On theother hand, the tin content should not exceed 3.0%, since theconductivity and the bending ability are negatively influenced thereby.In principle, the tin concentration is to be kept as low as possible;however, no substantial influence on the alloy properties can still beexpected at a proportion less than 0.3%

Iron is responsible for the formation of precipitation particles andtherefore provides an improvement of the relaxation properties incomparison to typical brasses. The precipitation formation can becontrolled and optimized during the manufacturing process. Inparticular, precipitants form in this alloy during a hot rolling stepwith a following targeted cooling. The annealing mechanisms active inthe alloy are primarily borne by the element iron.

The ferrous particles present in the alloy matrix form in thesubmicrometer range. The further elements optionally contained in thealloy can cause a further property improvement of the alloy with respectto the process control or can also display the effect thereof during theproduction process in the molten phase. A further key property is thebending ability in strips, which is improved in particular at higherzinc contents. The experimental results showed that both for low and forhigh zinc contents, approximately equal levels of residual stressesoccur in the alloy. It is essential that in the alloy according to theinvention, the relaxation resistance is significantly improved inrelation to the typical brasses and is only slightly below the typicalvalues for bronze. The present brass alloy is therefore in the range ofthe commercially available tin bronzes with respect to the relaxationresistance.

In the alloy according to the invention, particular weight is placed onthe microstructure thereof, which displays a special combination of maintexture orientations as a result of the processing steps. The texturearises in the manufacturing during the thermomechanical treatment as aresult of different rolling processes. Rolling shaping steps cancomprise, on the one hand, cold rolling steps and intermediate annealingsteps and, on the other hand, hot rolling processes in conjunction withfurther cold rolling steps and intermediate annealing steps. Theformation of the alloy according to the invention having the specifiedmain texture orientations must be adapted in processing technologyprecisely to the formation of the finely distributed ferrous particlesin conjunction with the respective degrees of rolling reduction. Theoptimum of the expected property combinations can only thus be achieved.

The desired material parameters are of interest in particular for thedesign of spring elements, for example, because the stiffness of thespring and the carrying capacity thereof are thus determined. A closerelationship exists between the resulting texture orientations and themechanical anisotropy resulting therefrom. Cubic face-centered metalstypically form two different texture types after a high degree ofrolling deformation as a function of the stacking fault energy thereof.In metals having moderate to high stacking fault energy, such asaluminum and copper, the so-called copper rolling texture is found,which is composed of the ideal orientations, the so-called brassorientation, and also the S orientation and the copper orientation. Thesecond limiting type is the so-called alloy rolling texture, which isformed by metallic materials of low stacking fault energy, which alsoincludes most copper alloys, and which substantially consists of thebrass orientation. Texture studies on copper and copper-zinc alloys andalso electron-microscope studies of copper and CuZn30 in recent timehave shown that CuZn30 behaves similarly at lower degrees of shapingwith respect to the microstructure and the texture formation to copperand the typical brass rolling texture first results at moderate to highdegrees of rolling as a result of the twin and shear band formationswhich then begin. At lower degrees of rolling, the occurrence of mixedtexture types is accordingly also to be expected in copper alloys havinglower stacking fault energy.

Therefore, in strips of the alloy according to the invention,particularly advantageous textures and directional dependences of themechanical properties result. Texture types as a mixed texture betweenthe limiting cases of a copper orientation, on the one hand, and a brassorientation, on the other hand, are formed by comparatively low degreesof rolling reduction. The respective advantageous properties resultingare directly dependent thereon.

The special advantage is that the resistance of the alloy according tothe invention with respect to stress relaxation is substantially betterthan tin-free and iron-free copper-zinc alloys and the alloysimultaneously has a lower metal value than copper-tin-phosphor alloys.Surprisingly, the Cu—Zn—Sn—Fe materials according to the invention alsodisplay more favorable strength reduction behavior than the tin bronzeused in comparable products. The strength loss resulting at thebeginning of the recrystallization is less in any case. The ferrousparticles present in the alloy matrix are certainly formed sufficientlysmall, in the submicron range, that good tin plating ability andprocessing ability to form a plug connector is ensured. In the presentmatrix composition, the desired intermetallic phases may form with thecopper of the alloy matrix during the hot-dip tin plating. Theadvantageous intermetallic phases also form uniformly on the entiresurface in the case of galvanic tin plating with a following reflowtreatment. An important requirement of the surface which can beuniformly tin plated is that the small particles do not experience anysubstantial elongation in the rolling direction in the matrix duringmechanical shaping by means of hot rolling or cold rolling. In contrastto higher iron proportions lying outside the solution according to theinvention, a line-shaped broadening of larger iron particles, whichinterferes with the tin plating, does not occur.

In a preferred embodiment of the invention, the content of tin can be0.7% to 1.5% and that of iron can be 0.5% to 0.7%. A lower tin contentin the specified limits is therefore particularly advantageous, becausein this way the conductivity and the bending ability of the alloy arefurther improved. The specified iron content is selected such thatparticularly fine ferrous particles form in the alloy matrix. However,these particles still have the size to substantially improve themechanical properties.

The zinc content can advantageously be between 21.5% and 31.5%. Inparticular in this range, it is still ensured that the desiredsingle-phase alloy consisting of alpha phase can be produced. Suchalloys can be shaped more easily and are still suitable for fineprecipitation distribution of the ferrous particles. Furthermore, thezinc content can advantageously be between 28.5% and 31.5%.

In a further advantageous embodiment of the invention, the ratio of theproportions of the main texture orientations of brass orientation andcopper orientation can be less than 1. In relation to the known brassalloys of similar composition, but without iron precipitants, thisquotient displays the special features of this alloy. While incomparable experiments, pure CuZn30 alloys have a quotient of greaterthan 1.2, the desired mechanical properties form in the strip materialat a smaller ratio of the brass orientation to the copper orientation.The level of the stiffness and the carrying capacity of spring materialsis thus determined.

The ratio of the proportions of the main texture orientations of brassorientation and copper orientation can advantageously be between 0.4 and0.90. Particularly favorable mechanical properties of the alloy areformed in the specified range.

In an advantageous embodiment of the invention, finely distributedferrous particles having a diameter less than 1 μm can be provided at adensity of at least 0.5 particles per μm² in the alloy matrix. Thecombination of the particle size and the distribution thereof in thealloy finally influences the mechanical properties. The described finedistribution having a diameter less than 1 μm is pronounced over 99% andis primarily defining for the advantageous properties. In the typicalcase, the mean particle diameter of the finely distributed ferrousparticles is even less than 50 to 100 nm. If such small particles aresubjected to mechanical forming by means of hot rolling or cold rolling,they do not experience any substantial stretching in the rollingdirection, from which the good tin plating ability of the surface thenresults.

The mean grain size of the alloy matrix can advantageously be less than10 μm. However, the mean grain size is more preferably at most 5 μm. Byway of the combination of the grain size of the alloy matrix inconjunction with the size of the finely distributed ferrous particlesand the distribution thereof, an optimum of the alloy properties may beachieved with respect to the mechanical carrying capacity, electricalconductivity, resistance against stress relaxation, and bending abilitythereof.

Further exemplary embodiments of the invention will be explained ingreater detail on the basis of Tables 1 to 4.

In the tables:

-   Table 1 lists the composition of the examined copper alloys in    wt.-%;-   Table 2 lists properties of the alloys according to Table 1 after    the last cold rolling to final thickness and annealing for 250° C./3    hours;-   Table 3 lists properties of the alloys according to Table 1 after    the last cold rolling to final thickness and annealing for 300° C./5    minutes;-   Table 4 lists main texture orientations in volume-percent of the    alloys from Table 3.

The composition of the individual examples and comparative examples canbe inferred from Table 1; the results of the final states are containedin Tables 2 and 3.

COMPARATIVE EXAMPLE 1 (CuZn23.5Sn1.0):—Fine-Grained

The alloy components were melted in the graphite crucible andsubsequently laboratory sample blocks were cast in steel ingot molds viathe Tammann method. The composition of a laboratory block sample was Cu75.47%-Zn 23.47%-Sn 1.06% (see Table 1). After the milling to 22 mmthickness, the samples were hot rolled at 700-800° C. to 12 mm andsubsequently milled to 10 mm.

After the cold rolling to 1.8 mm, the alloy was annealed at 500° C./3hours. A yield strength of 109 MPa was achieved at a grain size of 30-35μm and a conductivity of 26.5% IACS. After the subsequent cold rollingto 0.33 mm and annealing at 320° C./3 hours, the yield strength was 311MPa at a grain size of 2-3 μm and a conductivity of 27.3% IACS.

After the rolling to the final thickness and tempering at 300° C./5minutes, at a 24% preceding cold deformation, yield strengths wereachieved of 541 MPa at an A10 elongation of 19.3% and a conductivity of25.1% IACS. The minimum bending radius minBR in relation to the stripthickness t (minBR/t perpendicular/parallel) in the V-forging die was0.4/1.2. The stress relaxation resistance was 92.3% of the initialstress after 100° C./1000 hours and 82.1% after 120° C./1000 hours. Witha preceding cold deformation of 40%, yield strengths were achieved of622 MPa at an A10 elongation of 4.6%, a conductivity of 24.8% IACS, andminBR/t perpendicular/parallel of 1.5/7.5. The stress relaxationresistance was 90.2% of the initial stress after 100° C./1000 hours and79.8% after 120° C./1000 hours.

After the rolling to the final thickness and tempering at 250° C./3hours, with a 24% preceding cold deformation, yield strengths wereachieved of 586 MPa at an A10 elongation of 9.8% and a conductivity of25.3% IACS. The minimum bending radius in relation to the stripthickness (minBR/t perpendicular/parallel) in the V-forging die was0.4/2.8.

COMPARATIVE EXAMPLE 2 (CuZn23.5Sn1.0):—Coarse-Grained

The composition corresponds to that of comparative example 1, themanufacturing is the same as in comparative example 1 up to the coldrolling to 0.33 mm. However, the second annealing, in contrast tocomparative example 1, is not performed at 320° C./3 hours, but ratherat 520° C./3 hours.

After the annealing at 520° C./3 hours, the yield strength was 106 MPaat a grain size of 45 μm and a conductivity of 27.9% IACS.

After the rolling to the final thickness and tempering at 300° C./5minutes, at a 24% preceding cold deformation, yield strengths wereachieved of 378 MPa at an A10 elongation of 33.7% and a conductivity of26.9% IACS. The minimum bending radius in relation to the stripthickness (minBR/t perpendicular/parallel) in the V-forging die was2.4/1.6. The stress relaxation resistance is 94.7% of the initial stressafter 100° C./1000 hours and 93.0% after 120° C./1000 hours.

With a preceding cold deformation of 40%, yield strengths were achievedof 503 MPa at an A10 elongation of 10.2%, a conductivity of 26.5% IACS,and minBR/t perpendicular/parallel of 3.5/4.0. The stress relaxationresistance was 96.1% of the initial stress after 100° C./1000 hours and91.2% after 120° C./1000 hours.

After the rolling to the final thickness and tempering at 250° C./3hours, with a 24% preceding cold deformation, yield strengths wereachieved of 402 MPa at an A10 elongation of 29.5% and a conductivity of27.3% IACS. The minimum bending radius in relation to the stripthickness (minBR/t perpendicular/parallel) in the V-forging die was2.8/2.8. The stress relaxation resistance was 98.7% of the initialstress after 100° C./1000 hours and 93.5% after 120° C./1000 hours. Witha preceding cold deformation of 40%, yield strengths were achieved of517 MPa at an A10 elongation of 8.3%, a conductivity of 26.4% IACS, andminBR/t perpendicular/parallel of 4.5/6.0. The stress relaxationresistance was 96.8% of the initial stress after 100° C./1000 hours and91.9% after 120° C./1000 hours.

The comparison of comparative example 1 with comparative example 2shows, after the second annealing, a yield strength higher by 200 MPa ofthe fine-grained microstructure in comparison to the coarse-grainedmicrostructure. The following cold deformation reduces this differenceto still 160 MPa in the sample deformed by 24% and to 110 MPa in thesample deformed by 40%. In the final state after annealing at 300° C./5minutes, a comparable yield strength of approximately 520 MPa can beachieved both of the coarse-grained manufacturing (503 MPa) with a 40%rolling reduction and also of the fine-grained manufacturing (541 MPa)with a 24% rolling reduction. Simultaneously, however, the A10elongations in the fine-grained manufacturing are more favorable with19.3% in comparison to 10.2% in the coarse-grained manufacturing. Theminimum bending radii in relation to the strip thickness for thefine-grained manufacturing at 0.4/1.2 are similarly favorable incomparison to the coarse-grained manufacturing at 3.5/4. Only the stressrelaxation resistance is slightly more favorable for the coarse-grainedmicrostructure with 96.1% residual stress (fine-grained: 92.3% residualstress) after 100° C./1000 hours and with 91.2% residual stress(fine-grained: 82.1% residual stress) after 120° C./1000 hours.

EXAMPLE 3 (CuZn23.5Sn1.0Fe0.6):—Fine-Grained

The alloy components were melted in the graphite crucible andsubsequently laboratory sample blocks were cast in steel ingot molds viathe Tammann method. The composition of a laboratory block sample was Cu74.95%-Zn 23.40%-Sn 1.06%-Fe 0.59% (see Table 1). After the milling to22 mm thickness, the samples were hot rolled at 700-800° C. to 12 mm andsubsequently milled to 10 mm. The microstructure displayed smallerparticles, <1 μm, after the hot rolling. The <1 μm particles wereidentified as ferrous by means of EDX. After the cold rolling to 1.8 mm,the alloy was annealed at 500° C./3 hours. A yield strength of 304 MPawas achieved at a grain size of 5-15 μm and a conductivity of 24.2%IACS. After the subsequent cold rolling to 0.33 mm and annealing at 520°C./3 hours, the yield strength was 339 MPa at a grain size of 3-4 μm anda conductivity of 24.3% IACS.

After the rolling to the final thickness and tempering at 300° C./5minutes, at a 24% preceding cold deformation, yield strengths wereachieved of 623 MPa at an A10 elongation of 10.5% and a conductivity of22.9% IACS. The minimum bending radius in relation to the stripthickness (minBR/t perpendicular/parallel) in the V-forging die was2.4/3.6. The stress relaxation resistance was 90.7% of the initialstress after 100° C./1000 hours and 79.2% after 120° C./1000 hours.

With a preceding cold deformation of 40%, yield strengths were achievedof 686 MPa at an A10 elongation of 6.5%, a conductivity of 22.8% IACS,and minBR/t perpendicular/parallel of 4/10.

After the rolling to the final thickness and annealing at 250° C./3hours, with a 24% preceding cold deformation, yield strengths wereachieved of 632 MPa at an A10 elongation of 9.4% and a conductivity of23.2% IACS. The minimum bending radius in relation to the stripthickness (minBR/t perpendicular/parallel) in the V-forging die was3.2/4.8. The stress relaxation resistance was 90.8% of the initialstress after 100° C./1000 hours and 80.1% after 120° C./1000 hours. Witha preceding cold deformation of 40%, yield strengths were achieved of713 MPa at an A10 elongation of 2.8%, a conductivity of 23.0% IACS, andminBR/t perpendicular/parallel of 5/10.

In comparison to the fine-grained variant without Fe in comparativeexample 1, the ferrous fine-grained variant, after the final annealingat 300° C./5 minutes, displays a higher yield strength by 82 MPa (24%rolling reduction) or 64 MPa (40% rolling reduction), respectively.

With both alloy variants, a comparable yield strength of 620 MPa can beachieved, with different manufacturing, however. Thus,CuZn23.5Sn1.0Fe0.6 achieves a yield strength of 623 MPa after 24%rolling reduction and final annealing at 300° C./5 minutes andCuZn23.5Sn1.0 achieves a yield strength of 622 MPa after 40% rollingreduction and final annealing at 300° C./5 minutes. However, the A10elongations in the ferrous variant are higher at 10.5% in comparison to4.6% with CuZn23.5Sn1.0. The minimum bending radii in relation to thestrip thickness are similarly favorable for the ferrous variant at2.4/3.6 in comparison to the nonferrous variant at 1.5/7.5. The stressrelaxation resistance of both variants is similar, in contrast.

At an image enlargement of 5000:1 and 10,000:1, the number of particlesper 1 μm² image detail was counted, see figures 1 and 2. Themicrostructure of a surface grind was shown by means of an AsB detectoron the scanning electron microscope. The diameter of the majority of theiron particles is less than 200 nm, particles greater than 200 nm andless than 1 μm exist in isolation. The particle density is on average1.2/μm².

EXAMPLE 4 (CuZn23.5Sn1.0Fe0.6P0.2):—Fine-Grained

The alloy components were melted in the graphite crucible andsubsequently laboratory sample blocks were cast in steel ingot molds viathe Tammann method. The composition of a laboratory block sample is Cu74.77%-Zn 23.45%-Sn 1.04%-Fe 0.56%-P 0.19%, see Table 1. After themilling to 22 mm thickness, the samples were hot rolled at 700-800° C.to 12 mm and subsequently milled to 10 mm. The microstructure displayedsmaller particles, <1 μm. In addition, several coarser particles, >1 μm,are present in the matrix. The particles were identified asFeP-containing by means of EDX. After the cold rolling to 1.8 mm, thealloy was annealed at 500° C./3 hours. A yield strength of 293 MPa wasachieved in this case at a grain size of 10 μm and a conductivity of26.6% IACS. After the subsequent cold rolling to 0.33 mm and annealingat 370° C./3 hours, the yield strength was 393 MPa at a grain size of3-4 μm and a conductivity of 26.7% IACS.

After the rolling to the final thickness and tempering at 300° C./3hours, at a 24% preceding cold deformation, yield strengths wereachieved of 633 MPa at an A10 elongation of 11.6% and a conductivity of24.2% IACS. The minimum bending radius in relation to the stripthickness (minBR/t perpendicular/parallel) in the V-forging die was2/4.8. The stress relaxation resistance was 91.2% of the initial stressafter 100° C./1000 hours and 81.3% after 120° C./1000 hours. With apreceding cold deformation of 40%, yield strengths were achieved of 710MPa at an A10 elongation of 3.1%, a conductivity of 23.7% IACS, andminBR/t perpendicular/parallel of 3.5/11. The stress relaxationresistance was 90.1% of the initial stress after 100° C./1000 hours and79.6% after 120° C./1000 hours.

After the rolling to the final thickness and tempering at 250° C./3hours, with a 24% preceding cold deformation, yield strengths wereachieved of 641 MPa at an A10 elongation of 9.5% and a conductivity of23.6% IACS. The minimum bending radius in relation to the stripthickness (minBR/t perpendicular/parallel) in the V-forging die was 2/6.The stress relaxation resistance was 93.5% of the initial stress after100° C./1000 hours and 81.0% after 120° C./1000 hours. With a precedingcold deformation of 40%, yield strengths were achieved of 723 MPa at anA10 elongation of 1.4%, a conductivity of 23.8% IACS, and minBR/tperpendicular/parallel of 4.5/10.5. The stress relaxation resistance was92.9% of the initial stress after 100° C./1000 hours and 78.4% after120° C./1000 hours.

In comparison to the fine-grained variant in comparative example 1, theFeP-containing fine-grained variant, after the final annealing at 300°C./5 minutes, displays a higher yield strength by 92 MPa (24% rollingreduction) or 88 MPa (40% rolling reduction), respectively.

Both fine-grained alloy variants achieved a comparable yield strength of620-630 MPa in each case after a 24% rolling reduction and finalannealing at 300° C./5 minutes (CuZn23.5Sn1.0Fe0.6P0.2: Rp0.2=633 MPa)and after a 40% rolling reduction and final annealing at 300° C./5minutes (CuZn23.5Sn1.0: Rp0.2=622 MPa). However, the A10 elongations inthe FeP containing variant are higher at 11.6% in comparison to 4.6%with CuZn23.5Sn1.0. The minimum bending radii in relation to the stripthickness are similarly favorable for the FeP-containing variant at2.0/4.8 in comparison to the nonferrous variant at 1.5/7.5. The stressrelaxation resistance of both variants is similar.

EXAMPLE 5 (CuZn23.5Sn1.0Fe0.6P0.2):—Coarse-Grained

The composition corresponds to that of example 4, the manufacturing isthe same as in example 4 up to the cold rolling to 0.33 mm. However, thesecond annealing, in contrast to example 4, is not performed at 370°C./3 hours, but rather at 520° C./3 hours. A yield strength was achievedof 212 MPa in this case at a grain size of 10-25 μm and a conductivityof 26.7% IACS.

After the rolling to the final thickness and tempering at 300° C./5minutes, at a 24% preceding cold deformation, yield strengths wereachieved of 534 MPa at an A10 elongation of 23.1% and a conductivity of24.5% IACS. The minimum bending radius in relation to the stripthickness (minBR/t perpendicular/parallel) in the V-forging die was2.4/3.2. The stress relaxation resistance was 95.8% of the initialstress after 100° C./1000 hours and 90.9% after 120° C./1000 hours. Witha preceding cold deformation of 40%, yield strengths were achieved of634 MPa at an A10 elongation of 7.8%, a conductivity of 24.1% IACS, andminBR/t perpendicular/parallel of 3.5/8.5. The stress relaxationresistance was 93.9% of the initial stress after 100° C./1000 hours and85.2% after 120° C./1000 hours.

After the rolling to the final thickness and annealing at 250° C./3hours, at a 24% preceding cold deformation, yield strengths wereachieved of 544 MPa at an A10 elongation of 17.8% and a conductivity of24.7% IACS. The minimum bending radius in relation to the stripthickness (minBR/t perpendicular/parallel) in the V-forging die was3.2/4.0. The stress relaxation resistance was 95.1% of the initialstress after 100° C./1000 hours and 90.1% after 120° C./1000 hours. Witha preceding cold deformation of 40%, yield strengths were achieved of642 MPa at an A10 elongation of 4.3%, a conductivity of 24.0% IACS, andminBR/t perpendicular/parallel of 4.5/8.5. The stress relaxationresistance was 95.0% of the initial stress after 100° C./1000 hours and86.4% after 120° C./1000 hours.

The comparison of example 4 with example 5 shows, after the secondannealing, a yield strength higher by 180 MPa of the fine-grainedmicrostructure in comparison to the coarse-grained microstructure. Thefollowing cold deformation reduces this difference to 60 MPa in thesample deformed by 24% and to 40 MPa in the sample deformed by 40%.After the final annealing at 300° C./5 minutes, the difference of theyield strength between coarse-grained and fine-grained is 100 MPa(degree of deformation 24%) and 75 MPa (degree of deformation 40%).

In the final state after the annealing at 300° C./5 minutes, acomparable yield strength of approximately 630 MPa can be achieved bothof the coarse-grained manufacturing (634 MPa) with a 40% rollingreduction and also of the fine-grained manufacturing (633 MPa) with a24% rolling reduction. Simultaneously, however, the A10 elongations inthe fine-grained manufacturing are more favorable with 11.6% incomparison to 7.8% in the coarse-grained manufacturing. The minimumbending radii in relation to the strip thickness for the fine-grainedmanufacturing at 2.0/4.8 are similarly favorable in comparison to thecoarse-grained manufacturing at 3.5/8.5. Only the stress relaxationresistance is slightly higher for the coarse-grained microstructure with93.9% residual stress (fine-grained: 91.2% residual stress) after 100°C./1000 hours and with 85.2% residual stress (fine-grained: 81.3%residual stress) after 120° C./1000 hours.

EXAMPLE 6 (CuZn30Sn1.0Fe0.6):—Fine-Grained

The alloy components were melted in the graphite crucible andsubsequently laboratory sample blocks were cast in steel ingot molds viathe Tammann method. The composition of the laboratory block sample wasCu 68.26%-Zn 30.16%-Sn 1.03%-Fe 0.55%, see Table 1. After the milling to22 mm thickness, the samples were hot rolled at 700-800° C. to 12 mm andsubsequently milled to 10 mm. The microstructure displayed smallerparticles, <1 μm, after the hot rolling. The <1 μm particles wereidentified as ferrous by means of EDX. After the cold rolling to 1.8 mm,the alloy was annealed at 500° C./3 hours. A yield strength of 339 MPawas achieved in this case at a grain size of 5 μm and a conductivity of23.1% IACS.

In principle, in addition to the Tammann method mentioned in theexamples, other suitable casting methods can also be used. Strip castingalso comes into consideration in this context in particular.

After the subsequent cold rolling to 0.33 mm, a part was annealed at520° C./3 hours. A yield strength of 340 MPa was achieved in this caseat a grain size of 3-4 μm and a conductivity of 23% IACS.

After the rolling to the final thickness and tempering at 300° C./5minutes, at a 12% preceding cold deformation, yield strengths wereachieved of 486 MPa at an A10 elongation of 19.0% and a conductivity of22.2% IACS. The minimum bending radius in relation to the stripthickness (minBR/t perpendicular/parallel) in the V-forging die was 0/0.The stress relaxation resistance was 88% of the initial stress after100° C./1000 hours and 76.7% after 120° C./1000 hours.

With a preceding cold deformation of 18%, yield strengths were achievedof 550 MPa at an A10 elongation of 21.3%, a conductivity of 21.9% IACS,and minBR/t perpendicular/parallel of 0.9/0.4. The stress relaxationresistance was 88.3% of the initial stress after 100° C./1000 hours and75.6% after 120° C./1000 hours.

After the rolling to the final thickness and annealing at 250° C./3hours, with a 12% preceding cold deformation, yield strengths wereachieved of 505 MPa at an A10 elongation of 18.5% and a conductivity of22.6% IACS. The minimum bending radius in relation to the stripthickness (minBR/t perpendicular/parallel) in the V-forging die was 0/0.The stress relaxation resistance was 87.3% of the initial stress after100° C./1000 hours and 76.2% after 120° C./1000 hours. With a precedingcold deformation of 18%, yield strengths were achieved of 564 MPa at anA10 elongation of 19.9%, a conductivity of 22.2% IACS, and minBR/tperpendicular/parallel of 0.9/0.6. The stress relaxation resistance was88.4% of the initial stress after 100° C./1000 hours and 77.6% after120° C./1000 hours.

After the cold rolling to 0.33 mm, a further part was annealed at 450°C./30 seconds. A yield strength of 460 MPa was achieved in this case ata grain size of 1-2 μm and a conductivity of 22.6% IACS.

After the rolling to the final thickness and tempering at 300° C./5minutes, at a 24% preceding cold deformation, yield strengths wereachieved of 649 MPa at an A10 elongation of 9.0% and a conductivity of21.8% IACS. The minimum bending radius in relation to the stripthickness (minBR/t perpendicular/parallel) in the V-forging die was1.6/6.4. The stress relaxation resistance was 77.9% of the initialstress after 100° C./1000 hours and 61.0% after 120° C./1000 hours.

With a preceding cold deformation of 40%, yield strengths were achievedof 704 MPa at an A10 elongation of 2.9%, a conductivity of 21.5% IACS,and minBR/t perpendicular/parallel of 2/6.4. The stress relaxationresistance was 77.5% of the initial stress after 100° C./1000 hours and61.8% after 120° C./1000 hours.

After the rolling to the final thickness and annealing at 250° C./3hours, with a 24% preceding cold deformation, yield strengths wereachieved of 687 MPa at an A10 elongation of 3.9% and a conductivity of21.9% IACS. The minimum bending radius in relation to the stripthickness (minBR/t perpendicular/parallel) in the V-forging die was2/4.8. The stress relaxation resistance was 77.4% of the initial stressafter 100° C./1000 hours and 61.5% after 120° C./1000 hours. With apreceding cold deformation of 40%, yield strengths were achieved of 765MPa at an A10 elongation of 1.5%, a conductivity of 21.6% IACS, andminBR/t perpendicular/parallel of 4.0/9.2. The stress relaxationresistance was 76.8% of the initial stress after 100° C./1000 hours and59.9% after 120° C./1000 hours.

The microstructure of a surface grind was shown by means of a AsBdetector on the scanning electron microscope. At an image enlargement of5000:1 and 10,000:1, the number of particles per 1 μm² image detail wascounted. The diameter of at least 90% of the iron particles is less than200 nm. Iron particles having a diameter of 200 nm to 1 μm exist at lessthan 10%. The particle density is on average 0.9 particles per μm².

Further samples were also manufactured and tempered in the operatingscale. To evaluate the tin plating ability, a multiple wave solderingtest was carried out according to DIN EN 60068-2-20. The samples werepickled. The solder bath consisted of Sn60Pb40 at 235° C. The test wasperformed at an immersion speed of 25 mm/second and a dwell time of 5seconds, wherein pure rosin at 260 g/L was used as a flux. The sampleswere evaluated as good during the subsequent visual check.

By means of a Lücke-type goniometer, the main texture types wereascertained by x-ray diffractometry in all samples from Table 3 on the18%, 24%, and 40% cold-deformed plate annealed at 300° C./5 minutes. Forthis purpose, the intensity distributions of the skeleton lines in Eulerspace and the orientation distribution functions were analyzed. Theproportion of the copper orientation, S/R orientation, brassorientation, Goss orientation, 22RD cube orientation, and cubeorientation as the respective main texture orientations is shown inTable 4. The ratio of the volumes of the brass orientation to the copperorientation is less than 1 in all cases. For comparison, the ratio ofthe volume of the brass orientation to the copper orientation in thecomparative alloy CuZn30 has a value of 1.38 at a degree of rollingreduction of 47% during the final shaping. The designation S/Rorientation refers to the respective identical orientations originatingfrom the rolling texture or recrystallization texture in Euler space.The 22RD cube orientation designates a cube orientation rotated by ø=22°in Euler space. These designations have also become common for otherspecifications used in the literature in the meantime in practice forsample characterization.

COMPARATIVE EXAMPLE 7 (CuZn10Sn1.7Fe1.7P0.025)

127 mm×820 mm blocks of the composition Cu 86.29%-Zn 10.21%-Sn 1.70%-Fe1.74%-P 0.025% were extruded and hot rolled to 14.7 mm at 890° C. Afterthe cold rolling to 1.4 mm, annealing at 450° C./2 hours, cold rollingto 0.4 mm, annealing at 420° C./4 hours, rolling to 0.254 mm, andannealing at 280° C./4 hours, yield strengths of 633 MPa, an A10elongation of 8.7% and a minimum bending radius in relation to the stripthickness (minBR/t perpendicular/parallel) in the V-forging die of1.6/2.0 were achieved. Subsequently, the strips were hot-dip tin platedwith a layer thickness of 2-3 μm. The tin plating result is flawed,pores and stripes occur. The linear irregularities on the tin platedsurface originate from the elongated Fe lines, on which no Cu is presentto form an intermetallic phase.

COMPARATIVE EXAMPLE 8 CuZn23.5Sn1.0Fe2.0

The alloy components were melted in the graphite crucible andsubsequently laboratory sample blocks were cast in steel ingot molds viathe Tammann method. The composition of the laboratory block sample wasCu 73.82%-Zn 23.19%-Sn 1.04%-Fe 1.95%, see Table 1. After the milling to22 mm thickness, the samples were hot rolled at 700-800° C. to 12 mm.The microstructure displayed smaller particles, less than 1 μm,similarly to CuZn23.5Sn1.0Fe0.6. In addition, coarse particlesapproximately 5 μm in size were present in CuZn23.5Sn1.0Fe2.0. Both theparticles smaller than 1 μm and the particles 5 μm in size wereidentified as ferrous by means of EDX.

After the cold rolling to 1.8 mm, the alloy was annealed at 500° C./3hours. A yield strength of 362 MPa was achieved in this case at a grainsize of 2-3 μm and a conductivity of 24.2% IACS. After the subsequentcold rolling to 0.33 mm and annealing at 520° C./3 hours, the yieldstrength was 386 MPa at a grain size of 2 μm and a conductivity of 24.0%IACS.

After the rolling to the final thickness and tempering at 300° C./5minutes, at a 24% preceding cold deformation, yield strengths wereachieved of 642 MPa at an A10 elongation of 8.4% and a conductivity of23.1% IACS. The minimum bending radius in relation to the stripthickness (minBR/t perpendicular/parallel) in the V-forging die was 2/5.

With a preceding cold deformation of 40%, yield strengths were achievedof 712 MPa at an A10 elongation of 5.0%, a conductivity of 22.4% IACS,and minBR/t perpendicular/parallel of 2.5/9.

Elongated lines having a length of greater than 20 μm developed in thecourse of the further manufacturing from the particles of approximately5 μm in size present after the hot rolling.

To evaluate the tin-plating ability, a multiple wave soldering test wascarried out according to DIN EN 60068-2-20 on the samples tempered at300° C./5 minutes. The samples were pickled and brushed. The solder bathconsisted of Sn60Pb40 at 235° C. The test was performed at an immersionspeed of 25 mm/second and a dwell time of 5 seconds, wherein pure rosinat 260 g/L was used as a flux. The samples were evaluated as bad duringthe subsequent visual check as a result of strong dewetting.

The elongated ferrous lines are the cause of the poor tin platingability of the samples. No Cu is present thereon to form anintermetallic phase and undesired irregularities occur on the tin-platedstrips.

TABLE 1 composition of the copper alloys in wt.-% Cu, Zn, Sn, Fe, P,Nominal composition Example % % % % % CuZn23.5Sn1.0 compar- 75.47 23.471.06 ative example 1 compar- ative example 2 CuZn23.5Sn1.0Fe0.6 example3 74.95 23.40 1.06 0.59 CuZn23.5Sn1.0Fe0.6P0.2 example 4 74.77 23.451.04 0.56 0.19  example 5 CuZn30Sn1Fe0.6 example 6 68.26 30.16 1.03 0.55CuZn10Sn1.7Fe1.7P0.025 compar- 86.29 10.21 1.70 1.74 0.025 ative example7 CuZn23.5Sn1.0Fe2.0 compar- 73.82 23.19 1.04 1.95 ative example 8

TABLE 2 properties after the last cold rolling to final thickness andannealing 250° C./3 hours Hot rolling, 3 cold rolling steps, and finalannealing 250° C./3 hours Degree of rolling reduction final shaping, %Rp0.2, Rm, Grain minBR/t minBR/t Example ID % IACS MPa MPa size, μm Q PComparative CuZn23.5Sn1.0 24 25.3 586 641 2-3 0.4 2.8 example 1Comparative CuZn23.5Sn1.0 24 27.3 402 468 50 2.8 2.8 example 2 40 26.4517 566 45 4.5 6   Example 3 CuZn23.5Sn1.0Fe0.6 24 23.2 632 674Stretched 3.2 4.8 40 23   713 765 Stretched 5   10   Example 4CuZn23.5Sn1.0Fe0.6P0.2 24 23.6 641 703 1-2 2   6   40 23.8 723 783 1-24.5 10.5  Example 5 CuZn23.5Sn1.0Fe0.6P0.2 24 24.7 544 592 10-15 3.2 4  40 24   642 689  5-10 4.5 8.5 Example 6 CuZn30.0Sn1.0Fe0.6 18 22.2 564609  2 0.9 0.6 24 21.9 687 748 1-2 2   4.8 40 21.6 765 829  2 4   9.2

TABLE 3 properties after the last cold rolling to final thickness andannealing 300° C./5 minutes Hot rolling, 3 cold rolling steps, and finalannealing 300° C./5 minutes Degree of rolling Grain reduction final %Rp0.2, Rm, size, minBR/t minBR/t Example ID shaping, % IACS MPa MPa μm QP Comparative CuZn23.5Sn1.0 24 25.1 541 604 2-3 0.4 1.2 example 1 4024.8 622 694 2-3 1.5 7.5 Comparative CuZn23.5Sn1.0 24 26.9 378 454 40-502.4 1.6 example 2 40 26.5 503 557 40 3.5 4 Example 3 CuZn23.5Sn1.0Fe0.624 22.9 623 667 2-3 2.4 3.6 40 22.8 686 742  3 4 10 Example 4CuZn23.5Sn1.0Fe0.6P0.2 24 24.2 633 699 1-2 2 4.8 40 23.7 710 756 1-2 3.511 Example 5 CuZn23.5Sn1.0Fe0.6P0.2 24 24.5 534 580 10-15 2.4 3.2 4024.1 634 675  5-10 3.5 8.5 Example 6 CuZn30.0Sn1.0Fe0.6 18 21.9 550 6062-3 0.9 0.4 24 21.8 649 720 1-2 1.6 6.4 40 21.5 704 782  2 2 6.4

TABLE 4 main texture orientations in volume percent of the alloys fromTable 3 Hot rolling, 3 cold rolling steps, and final annealing 300° C./5minutes 22RD Degree of Copper S/R Brass Goss cube Cube Brass/ rollingorien- orien- orien- orien- orien- orien- Copper reduction, tationtation tation tation tation tation orien- Example ID % vol.-% vol.-%vol.-% vol.-% vol.-% vol.-% tation Comparative CuZn23.5Sn1.0 24 14.715.4  8.8 4.4 5.3 2.0 0.60 example 1 40 14.5 16.0 10.0 5.0 4.7 1.4 0.69Comparative CuZn23.5Sn1.0 24 14.9 15.0  7.9 4.1 5.2 1.8 0.53 example 240 12.1 18.2  9.7 7.5 4.7 0.9 0.80 Example 3 CuZn23.5Sn1.0Fe0.6 24 17.819.8  9.4 4.5 4.0 1.2 0.53 Example 4 CuZn23.5Sn1.0Fe0.6P0.2 24 15.9 15.411.3 5.7 3.5 1.3 0.71 Example 5 CuZn23.5Sn1.0Fe0.6P0.2 24 17.7 17.3  8.87.5 4.4 1.0 0.50 Example 6 CuZn30.0Sn1.0Fe0.6 18 15.3 17.6  8.1 2.9 4.22.1 0.53 24 12.1 16.8 10.2 3.7 4.4 2.3 0.84

The invention claimed is:
 1. A copper alloy, which was subjected to athermomechanical treatment, consisting of, in wt. %: 28.5 to 31.5% Zn,0.3 to 3.0% Sn, 0.55 to 0.7% Fe, optionally 0.001 to 0.4% P, optionally0.01 to 0.1% Al, optionally 0.01 to 0.3% Ag, 0.01 to 0.3% Mg, 0.01 to0.3% Zr, 0.01 to 0.3% In, 0.01 to 0.3% Co, 0.01 to 0.3% Cr, 0.01 to 0.3%Ti, and 0.01 to 0.3% Mn, optionally 0.05 to 0.5% Ni, the remainder beingcopper and unavoidable impurities, wherein the microstructure of thealloy is characterized in that the proportions of the main textureorientations are at least 10 vol.-% copper orientation, at least 10vol.-% SIR orientation, at least 5 vol.-% brass orientation, at least 2vol.-% Goss orientation, at least 2 vol.-% 22RD cube orientation, atleast 0.5 vol.-% cube orientation, and finely distributed ferrousparticles are contained in the alloy matrix.
 2. The copper alloy asclaimed in claim 1, characterized by a content of 0.7 to 1.5% Sn.
 3. Thecopper alloy as claimed in claim 1, characterized in that the ratio ofthe proportions of the main texture orientations of brass orientationand copper orientation is less than
 1. 4. The copper alloy as claimed inclaim 3, characterized in that the ratio of the proportions of the maintexture orientations of brass orientation and copper orientation isbetween 0.4 and 0.90.
 5. The copper alloy as claimed in claim 1,characterized in that finely distributed ferrous particles having adiameter less than 1 μm are present at a density of at least 0.5particles per μm² in the alloy matrix.
 6. The copper alloy as claimed inclaim 1, characterized in that the mean grain size of the alloy matrixis less than 10 μm.